1. Field of the Invention
This invention relates to a solid detergent composition, more particularly to a solid detergent composition which maintains its shape during use with no swelling, liquidification or cracking and which has a refreshing feel and good detergency.
2. Description of the Background Art
Typical solid detergents include 1) standard soap which is an alkali salt of a higher fatty acid, 2) combar which is a soap containing a synthetic surfactant, and 3) syndet bar which is prepared by binding synthetic surfactants with a binder.
Standard soaps are generally prepared either by allowing a mixture of oils and/or fats such as beef tallow and coconut oil to react with an aqueous solution of caustic soda, or by a method where a fatty acid mixture obtained from the decomposition of beef tallow, coconut oil and the like is neutralized with caustic soda, caustic potash, alkanolamine or the like to obtain a soap base, followed by the addition of perfumes and colorants. Recently, super-fat soaps which contain a free fatty acid have become the main product of the industry. The synthetic surfactants which are contained in a combar and a syndet bar include isethionic esters, alcohol sulfate, alcohol phosphate and N-acylglutamate.
Solid detergent compositions are essentially water-soluble, and therefore, they absorb water when they are repeatedly used in the bath, in lavatories and the like. This water absorption causes swelling, induces softening and melt-off, and brings about the occurrence of cracks, all resulting in a composition with unfavorable appearance and texture. Furthermore, the softening/swelling of a detergent article leads to deteriorated foam-producing ability and detergency.
Heretofore, only a few studies have been reported regarding the prevention of swelling, softening and melt-off, and the occurrence of cracks of solid detergent compositions: Japanese patent application laid-open to the public (Kokai) No. 58-167700 discloses a solid detergent composition having a cationic polymer and Japanese patent application laid-open to the public (Kokai) No. 62-199699 discloses a solid detergent composition having lactic acid or its salts. These detergent additives, however, are water-soluble, and therefore they are useless for preventing the above-mentioned defects like swelling.
Talc powder or kaolin powder has been incorporated into solid detergent compositions in an attempt to improve detergency and feel upon use. In this regard, U.S. Pat. No. 4557853 discloses a solid detergent composition incorporating calcium carbonate Japanese patent application lad-open to the public (Kokai) Nos. 58-191799, 62-43497, 62-70308 and others disclose solid detergent compositions incorporating an organic powder; and Japanese patent application laid-open to the public (Kokai) No. 61-275394 discloses a solid detergent composition incorporating water-insoluble synthetic amorphous granular silica or silicate. However, none of these additives prevented the detergent compositions form being softened/swollen, from melting off and softening or cracking, though the detergency and feel upon use were improved.
Accordingly, solid detergent compositions which will not be softened/swollen, not show melt-off, and not crack during use which also provide a refreshing feeling and excellent detergency are still sought after. Under these circumstances, the present inventors have conducted careful studies and have found that when specified metal oxides are incorporate into a solid detergent composition singly or in combination, the above-mentioned problems could be solved. The present invention was achieved based on this finding.